Problem: Admins, patrollers, and other editors often find useful to find out whether someone has been blocked elsewhere, or which other wikis they're active in. However, there are no easy links to Special:CentralAuth in the interface.
Who would benefit: Admins, patrollers, translators, community event organizers, and anyone who needs to find someone who is familiar with a different language or different wiki. (Also, in a more light-hearted way, it will be convenient for anyone who wants to check their own edit count total across all the wikis. This is not an important use, but sometimes it's fun to discover that you've passed a milestone number.)